This invention relates to a semiconductor pressure sensor and more particularly to a semiconductor pressure sensor useful in detecting pressure difference in two fluids.
One example of the conventional semiconductor pressure sensor is disclosed in Japanese Patent Laid-Open No. 60-100026 for example, in which two sets of semiconductor pressure sensing units each including a diaphragm portion and four piezo-electric resistor elements connected in a bridge circuit are formed on a single common semiconductor substrate, and in which the fluid of which pressure is to be measured is applied to one of the pressure sensing units and two outputs from the respective bridge circuits are compared to make a substraction, whereby any error due to residual distortions can be eliminated.
Another example of a semiconductor pressure sensor is disclosed in Japanese U. M. Laid-Open No. 61-87338. In this conventional pressure sensor, an opening is provided at the central portion of a base and a pressure introducing conduit extends downwardly from the opening, and other openings for atmospher are disposed remotely from the central opening. A pressure sensing diaphragm for detecting the pressure difference between the pressure introducing conduit and the atmospheric pressure is centrally disposed, and the opening for the atmospheric pressure is covered by the semiconductor chip which is covered by a cap.
Since the conventional semiconductor pressure sensors are constructed as above described, the sensitivities of the pressure sensing diaphragm and the control circuit must be made extremely high in order to detect a very small pressure. When the sensitivity of the pressure sensor is increased too much, the pressure sensor becomes too sensitive to responds even to the acceleration or vibration acting on the diaphragm of the sensor, providing an erroneous pressure signal.